There are several types of satellites deployed into orbit around the earth. Some satellites reflect communications directed at the satellite. Many satellites carry repeaters for receiving and retransmitting a received communication. In recent years, satellites have been placed in orbits synchronous with the earth's rotation, thereby providing continuous communications capabilities in almost all regions of the globe.
If a satellite is placed in synchronous orbit above the equator to revolve in the same direction of the earth's rotation and synchronized with the earth's rotation, the satellite will continually remain above a fixed point on the surface of the earth. Many communications satellites have been placed in these synchronous orbits to cover different regions of the globe.
Generally, active communications satellites are orbiting repeaters with broadband characteristics. A signal from a ground station is intercepted by the satellite, converted to another frequency, and retransmitted at a moderate power level to an end user receiver. This provides much better signal strength at the receiving end of the circuit as compared with a signal that is merely reflected from a passive satellite. Active communications satellites are placed in synchronous orbits, making it possible to use them with fixed antennas, a moderate level of transmitter power, and at any time of the day or night. Synchronous satellites are used for television and radio broadcasting, communications, weather forecasting, and military operations.
Further, a constellation of satellite systems is used to cover major regions of the globe to enable ground-to-aircraft (and aircraft-to-ground) communications via the satellite systems. One example of such a constellation is INMARSAT III, which currently comprises four satellites located in geostationary orbits, each generally covering a region of approximately one-fourth of the globe with a certain amount of overlap between regions. These satellites are referred to as AOR-W (Atlantic Ocean Region—West), AOR-E (Atlantic Ocean Region—East), IOR (Indian Ocean Region), and POR (Pacific Ocean Region). Another satellite constellation example is INMARSAT IV, which will comprise three satellites providing the same coverage as the four INMARSAT III satellites it will replace as well as additional services, such as Broadband Global Area Network (BGAN) and Swift Broadband (SBB).
INMARSAT satellites support various different types of communications services to the aeronautical market. These services are currently defined as AERO H, AERO H+, AERO I, Swift 64, and AERO M. SBB will also soon be available and is similar to BGAN but designed for AERO. All of these services are generally available to aeronautical users. An airborne satellite communication system can provide an aircraft with multiple digital voice, fax, and real-time Internet communications capabilities. These systems are specifically adapted for use in global two-way, ground-to-air communications by aircraft operators requiring global voice, fax, and Internet communications for their flight crews and passengers.
As the general communications need to transmit more data in larger files at faster speeds grows, so too does the need for faster connections and increased data throughput. This holds true for any communications system, whether strictly ground-based, air-to-ground, or ground-to-air. One way developers of ground-based systems have addressed this need is through the use of acceleration and compression technologies. Acceleration and compression can be achieved through any number of techniques to reduce data traffic volumes such as selective caching, vertical data analysis, adaptive packet compression, packet aggregation and flow control, and so on. This ground-based technology contributes to increasingly faster connection speeds.
Current ground stations have yet to implement acceleration technologies, however, and typically only provide connection speeds of 33.6 kbps on a single Mobile Packet Data Service (MPDS) channel, or up to 256 kbps on a four-channel system. For example, one current method for obtaining greater speeds in a Swift 64 ground-to-air communication system is to install additional Swift 64 units on the aircraft and combine the units to create a higher speed connection. This method of using more channels, without increasing the data transfer rate across any individual channel, may increase overall connection speed, but not in an efficient, cost-effective manner.
The same need for high-speed data connections that currently exists in the office or at home also exists in aircraft cabins. Until now, however, ground stations that support global two-way, air-to-ground (ATG), and ground-to-air (GTA) communications have not offered equivalent increases in data rates, and especially not in a cost-effective way.